1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device having a flexible seal member and, more particularly, to a LCD device including: a light source unit having a light-emitting surface; a LCD panel mounted on the light-emitting surface and configured to have a light switching function; and a frame-shaped shield front which defines the front screen of the LCD panel.
2. Description of the Related Art
A LCD device typically has a structure in which a panel assembly (LCD panel assembly) is held and fixed between a light source unit (backlight unit) and a shield front. FIG. 13 is a perspective view showing the configuration of a conventional LCD device as viewed from the front screen side. FIG. 14 is an exploded perspective view showing the LCD device of FIG. 13.
A LCD device 100 is provided with a light source unit 11 having a rectangular light-emitting surface 11a on the front side thereof, a panel assembly 12 mounted on the light-emitting surface 11a and configured to have a light switching function, and a frame-shaped shield front 13 which defines the front screen 13a for the panel assembly 12.
The panel assembly 12 is provided with a display panel 21 in which a TFT substrate 25 and a counter substrate 26 overlap with each other, a plurality of TCPs (Tape Carrier Packages) 22 coupled to the display panel 21, and a circuit board 23 mechanically and electrically coupled to the display panel 21 via the TCP 22. The TCPs 22 each mount thereon an IC chip for driving the display panel 21, and the circuit board 23 outputs a control signal for controlling the drive of the display panel 21 by the TCP 22. The TCP 22 and circuit board 23 are arranged along, e.g., two adjacent edges of the display panel 21.
The display panel 21 is provided with a liquid crystal (LC) layer (not shown) sandwiched between the TFT substrate 25 and the counter substrate 26, and polarization films (not shown) disposed on the rear surface of the TFT substrate 25 and the front surface of the counter substrate 26. The display panel 21 has pixels arranged in a two-dimensional matrix. On the TFT substrate 25, switching devices such as TFTs (Thin Film Transistors) are arranged in a matrix for controlling the switching of respective pixels to configure an active matrix substrate. On the counter substrate 26, color filters (CF) of different colors corresponding to the respective pixels are formed to configure a color-filter substrate (CF substrate) 26. Driving of the TFT devices via the circuit board 23 and TCP 22 achieves control of the panel assembly in a pixel-by-pixel basis.
The light source unit 11, which is, e.g., an edge-light-type backlight unit, has a frame-shaped chassis 31 for defining the light-emitting surface 11a on the front side thereof. On the chassis 31, ribs 32 are arranged for defining the position of the display panel relative to the light-emitting surface 11a and formed integrally with the chassis 31. The ribs 32 are arranged near the four corners of the light-emitting surface 11a. Each of the ribs 32 has an elongate rectangular solid shape which is bent at right angles along the corner of the display panel.
FIG. 15 is a sectional view taken along XV-XV line shown in FIG. 13. The light source unit 11, or the edge-light backlight unit, has an optical sheet 33, an optical guide plate 34 and a reflection sheet 35, which are sequentially stacked on the light-emitting surface 11a of the light source unit, as viewed from the front side. Further, an elongate lamp (not shown) is provided on the side edge of the optical guide plate 34. The optical guide plate 34 diffuses the light entering the optical guide plate 34 from the elongate light source in the in-plane direction thereof, to thereby convert the elongate light into a planar light. The reflection sheet 35 reflects the light emitted from the rear surface of the optical guide plate 34 toward the front surface of the light source unit 11. The optical sheet 33 has a function of enhancing brightness or luminance of the light-emitting surface 11a and uniformity of the luminance.
The chassis 31 has, around the light-emitting surface 11a, a flat mounting surface 36 on which the TFT substrate 25 is mounted and a concaved portion 37 which is formed nearer to the light-emitting surface 11a than the mounting surface 36 and receives therein the polarization film 27. The ribs 32 each have a position-restricting wall 32a which is located opposite to the side edge of the display panel so as to restrict the position of the display panel and an inclined surface 32b which extends from the edge of the position-restricting wall 32a in order for the display panel to be easily mounted on the light source unit 11. The chassis 31 is accommodated in a shield rear 38 of which top surface is open; and the optical sheet 33, optical guide plate 34, and reflection sheet 35 are disposed between the chassis 31 and the shield rear 38. Reference numerals 29 and 30 denote a seal member for sealing the LC layer 24 and the boundary of the display area, respectively.
During assembly of the LCD device 100, the position of the panel assembly 12 is first adjusted in the in-plane direction thereof with respect to the light source unit 11 such that the four corners of the display panel of the panel assembly are located within the area defined by the ribs 32 and, then, the panel assembly 12 is mounted on the light source unit 11. More specifically, the TFT substrate 25 of the panel assembly 12 is mounted on the mounting surface 36 of the chassis 31 with the polarization film 27 received in the concaved portion 37 of the chassis 31. Thereafter, the shield front 13 is placed to cover the light source unit 11 and panel assembly 12 to press the panel assembly 12 down to a predetermined position to thereby complete the assembly. Fixation between the light source unit 11 and the shield front 13 is achieved by screwing, caulking, or pawl engagement.
The conventional LCD device 100 has a disadvantage in that adhesion of dust onto the light-emitting surface 11a of the light source unit causes a defective image on the screen. That is, the shadow of the dust is projected on the screen 13a. This defective image is caused by the following factors. In the LCD device 100, a gap of 0.2 to 0.3 mm is intentionally provided between the side edge of the display panel 21 and the ribs 32, in consideration of the range of variation in the outside dimension of the display panel 21 and the range of variation in the distance between the ribs 32. Further, in consideration of the range of variation in the thickness dimension or distortion of the light source unit 11 or shield front 13, a gap of 0.1 to 0.3 mm is provided between the display panel 21 and the shield front 13 so as to prevent the inner surface of the shield front 13 from being brought into contact with the display panel 21. Thus, the display panel 21 or panel assembly 12 is movable within these gaps in the thickness direction and in-plane directions, as denoted by arrows of reference numeral 101.
As described above, in the conventional LCD device 100, the display panel 21 is provided in the movable state between the light source unit 11 and the shield front 13. Therefore, as shown by a reference numeral 102, dust enters the rear side of the display panel 21 through the gap between the display panel 21 and the shield front 13 and the gap between the display panel 21 and the chassis 31 of the light source unit 11. The dust that has entered the rear side of the display panel 21 is then adhered onto the light-emitting surface 11a of the light source unit 11.
As a countermeasure against the above disadvantage, there is known a method that provides a sealing member 103 in the gap between the display panel 21 and the shield front 13, as shown in FIG. 16. A LCD device in which the sealing member 103 is provided in the gap between the display panel and the shield front is described in, for example, Patent Publication JP-2005-91971A (FIG. 1).
In the LCD device 110 shown in FIG. 16, the gap between the display panel 21 and the shield front 13 is sealed by the sealing member 103. The sealing member 103 cuts off the entry route of the dust, thereby blocking the entrance of the dust.
However, in the LCD device 110 of FIG. 16, a significant range of variation occurs in the gap distance between the display panel 21 and the shield front 13 due to the variation in the outside dimension or distortion of the light source unit 11 or shield front 13. Accordingly, in order to surely block the entry route of the dust, it is necessary to form the sealing member 103 using a flexible material and makes the thickness thereof sufficiently large in consideration of the range of variation in the gap distance. However, examinations conducted by the present inventor revealed that a larger thickness of the sealing member 103 changes the gap distance of the LC layer 24 because the sealing member 103 presses the display panel 21 in the thickness direction thereof, thereby causing an uneven image on the screen. In order to achieve a LCD device having an excellent image quality, it is essential to prevent entrance of the dust into the rear side of the display panel while suppressing occurrence of the uneven image.